Studies on the behaviour of furalaxyl on pythiaceous fungi and cucumbers in recirculating hydroponic systems

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Abstract
Etridiazole and furalaxyl inhibited growth of Pythium irregulare in agar at 0.1 and 1 mg l-1, respectively, but sporulation was not inhibited by 10 and 5 mg I-'. In stationary hydroponic nutrients, recovery of P. irregulare declined with increasing concentrations of etridiazole and furalaxyl above 10 mg l-1 and with increasing duration of exposure to concentrations below 10 mg l-1. Zoospores of Phytophthora cryptogea were dispersed throughout recirculating nutrient film (NFT) systems, but few were recovered by plating nutrients sampled 1 h after inoculation. The fungus was detected by baiting nutrients up to 5 days after inoculation, but was not detected in nutrients treated with 20 mg l-1 furalaxyl. Concentrations of furalaxyl in the NFT system declined by 50% over 7 days. Furalaxyl significantly increased sodium levels in the NFT nutrients. Cucumber plants growing in furalaxyl-treated nutrients contained significantly higher levels of sodium and iron and decreased levels of zinc; fruit yields were significantly decreased but there were no effects on leaf or stem dry matter. Disease did not develop on cucumber plants growing in an NFT system inoculated with P. cryptogea. Pot experiments indicated the fungus was pathogenic at temperatures of 10/15¦C, and seed treatment with thiram was ineffective in controlling the pathogen. The management of P. cryptogea in NFT systems by furalaxyl or controlled environments is discussed.